Why is :box not getting the current background color?. It doesn't even work if I setq a variable with the color hardcoded, but if I set the hex color as a literal it works perfectly. If I evaluate manually the sexp (face-background 'default) it returns the right color #1E1C31 ( a dark color, but if you notice on the screenshot is setting a bright color ).

(set-face-attribute 'tab-bar-tab-inactive nil
  :family "Cascadia"
  :foreground (face-foreground 'default)
  :background (face-background 'default)
  :height 1.3
  :slant 'italic
  :box '(:line-width 9 :color (face-background 'default))

                        )